High-performance n-Si/α-Fe2O3 core/shell nanowire array photoanode towards photoelectrochemical water splitting†
Many narrow band-gap semiconductors cannot fulfil the energetic requirements for water splitting, thus the assistance of large external voltages to complete the water decomposition reaction is required. Through thermal decomposition of Fe(NO3)3 on n-Si nanowires prepared by the chemical etching method, we fabricated a high-performance n-Si/α-Fe2O3 core/shell nanowire array photoanode that exhibited a low photocurrent onset potential of 0.5 V vs. RHE and a high photocurrent of 5.28 mA cm−2 at 1.23 V vs. RHE, under simulated AM 1.5G irradiation. The photocurrent onset potential represents one of the lowest in n-Si or α-Fe2O3 based photoanodes, and the photocurrent is much larger than most of those observed on α-Fe2O3. The impact of the thickness of the α-Fe2O3 shell on the photoelectrochemical performance of the present photoanode was investigated in detail. It was found that both the photocurrent and the onset potential depend strongly on the α-Fe2O3 shell thickness. Mott–Schottky measurements and energy band calculation reveal that the energy band edge positions of the n-Si are closely related to the thickness of the α-Fe2O3. The α-Fe2O3 shell with an optimized thickness is favorable for locating the energy bands of the n-Si at relatively high levels and maximizing the charge collection in α-Fe2O3, and thus achieving the low photocurrent onset potential and high photocurrent.